Stretchable radial spare tire

Abstract

A radial spare tire which, upon inflation, stretches from a shape having a reduced diameter adjacent the wheel rim on which the tire is mounted, to a regularly sized radial tire which the spare tire is designed to replace. The tire is molded and vulcanized in an unstretched configuration of reduced size. The stretching of the tire is made possible by the utilization in the carcass and belt plies of reinforcement cords which, during the processing of the cord and building of the tire, have a relatively high modulus of elasticity. When the cords are subjected to vulcanization temperatures, they lose their strength and have a low modulus of elasticity to permit the stretching of the tire to a regular size. The cords then develop a high modulus of elasticity in the stretched condition to provide the required reinforcement of the tire in the inflated regular size condition.

What is claimed is: 
     
       1. A stretchable tire, comprising: (a) at least one carcass ply reinforced with radially oriented cords disposed at angles in the range of from 75-90 degrees relative to a centerplane containing the mid-circumferential centerline of the tread of the tire when the tire is molded, vulcanized and uninflated in a storage shape, said cords of said carcass ply being highly elongatable in an amount of from 50 to 100 percent to allow for toroidal expansion of the tire to an inflated operating shape;   (b) a fluid impervious innerliner disposed at the radially inner surface of said tire within said carcass ply;   (c) a tread and pair of sidewalls surrounding said carcass ply and terminating at a pair of annular beads;   (d) at least one belt ply of cords interposed between said carcass ply and tread for annularly reinforcing the tire, said cords of said belt ply being disposed at angles in the range of from 0-30 degrees measured from said centerplane when the tire is molded, vulcanized and uninflated in said storage shape, and also being highly elongatable in an amount of from 50 to 100 percent to allow for circumferential expansion of the tread upon inflation of the tire to said inflated operating shape;   (e) each of said reinforcement cords of said carcass ply and said belt ply consisting of a central core and at least one inextensible yarn spirally wrapped around said core, the tensile strength of said core being sufficient prior to being subjected to temperatures of vulcanization to maintain said inextensible yarn in helical relation during building of the tire and shaping to said storage shape from an unvulcanized cylindrical shape; and   (f) said core being of a material having a sufficient reduction in tensile strength when subjected to temperatures of vulcanization of the tire to permit the stretching out of said yarn after the tire is vulcanized and during expansion of the tire from said deflated storage shape with said yarn in the spirally wrapped condition to said inflated operating shape with said yarn in the stretched out condition.   
     
     
       2. The tire of claim 1, wherein said core is composed of a polymer of the group of polyolefines. 
     
     
       3. The tire of claim 2 wherein said polyolefines include polyethylene and polypropylene. 
     
     
       4. The tire of claim 1, wherein said inextensible yarn consists of at least one twisted strand composed of filaments of material of the group of rayon, nylon, polyester, aramid and steel. 
     
     
       5. The tire of claim 1, which includes two carcass plies reinforced with radially oriented cords, and two belt plies of cords between the tread and radially outermost ply of said carcass plies, said cords of said belt plies crossing and being disposed at identical cord angles measured in opposite directions from said centerplane. 
     
     
       6. The tire of claim 1, wherein said cords of said carcass ply and belt ply are each characterized after vulcanization by an initial low modulus of elasticity and high elongation and subsequent high modulus of elasticity and low elongation after said cords elongate a predetermined amount. 
     
     
       7. The tire of claim 1, wherein said cords of said carcass ply and belt ply are embedded in rubber material having a modulus of elasticity less than 150 kg/cm 2  at 100 percent elongation. 
     
     
       8. The tire of claim 1, wherein said core has a tensile strength of 10 kilograms prior to vulcanization and said reduction in tensile strength at temperatures of vulcanization is from 10 kilograms to zero or a negligible amount. 
     
     
       9. The tire of claim 1, wherein said core consists of a monofilament.